Method and apparatus for resume procedure for data transfer in rrc_inactive state in mobile wireless communication system

ABSTRACT

A method and apparatus for data transfer in RRC_INACTIVE state is provided. Method for data transfer in RRC_INACTIVE state includes receiving a RRCRelease, determining a radio bearer configured for second resume procedure based on the first information for second resume procedure, receiving from the base station a system information, initiating second resume procedure, restoring configuration of the radio bearer configured for second resume procedure stored in UE Inactive AS context, re-establishing PDCP entity of the radio bearer configured for second resume procedure, resuming the radio bearer configured for second resume procedure and transmitting to the base station a RRCResumeRequest.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a US Bypass Continuation Application ofInternational Application No. PCT/KR2022/011385, filed on Aug. 2, 2022,which claims priority to and the benefit of Korean Patent ApplicationNo. 10-2021-0108996, filed on Aug. 18, 2021, the disclosure of which isincorporated herein by reference in its entirety.

BACKGROUND

To meet the increasing demand for wireless data traffic since thecommercialization of 4th generation (4G) communication systems, the 5thgeneration (5G) system is being developed. For the sake of high, 5Gsystem introduced millimeter wave (mmW) frequency bands (e. g. 60 GHzbands). In order to increase the propagation distance by mitigatingpropagation loss in the 5G communication system, various techniques areintroduced such as beamforming, massive multiple-input multiple output(MIMO), full dimensional MIMO (FD-MIMO), array antenna, analogbeamforming, and large-scale antenna. In addition, base station isdivided into a central unit and plurality of distribute units for betterscalability. To facilitate introduction of various services, 5Gcommunication system targets supporting higher data rate and smallerlatency.

SUMMARY

Aspects of the present disclosure are to address the problems of statetransition from RRC_INACTIVE to RRC_CONNECTED for data transfer.Accordingly, an aspect of the present disclosure is to provide a methodand an apparatus for data transfer in RRC_INACTIVE state. In accordancewith an aspect of the present disclosure, a method of a terminal inmobile communication system is provided. The method comprises receivinga RRCRelease, determining a radio bearer configured for second resumeprocedure based on the first information for second resume procedure,receiving from the base station a system information, initiating secondresume procedure, restoring configuration of the radio bearer configuredfor second resume procedure stored in UE Inactive AS context,re-establishing PDCP entity of the radio bearer configured for secondresume procedure, resuming the radio bearer configured for second resumeprocedure and transmitting to the base station a RRCResumeRequest.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram illustrating the architecture of an 5G system and aNG-RAN to which the disclosure may be applied;

FIG. 1B is a diagram illustrating a wireless protocol architecture in an5G system to which the disclosure may be applied;

FIG. 1C is a diagram illustrating an RRC state transition.

FIG. 2A is a diagram illustrating operations of a terminal and a basestation according to an embodiment of the present invention.

FIG. 2B is a diagram illustrating a first resume procedure and a secondresume procedure according to an embodiment of the present invention.

FIG. 2C is a diagram illustrating a structure of an uplink MAC PDU usedin a second resume procedure.

FIG. 2D is a diagram illustrating a structure of a general uplink MACPDU.

FIG. 2E is a diagram illustrating a hierarchical structure of securitykeys.

FIG. 2F is a diagram illustrating structures of a first BSR MAC CE and asecond BSR MAC CE.

FIG. 2G is a diagram illustrating structures of a third BSR MAC CE and afourth BSR MAC CE.

FIG. 2H is a diagram illustrating a MAC-I calculation process andciphering process.

FIG. 3 is a flow diagram illustrating an operation of a terminal.

FIG. 4A is a block diagram illustrating the internal structure of a UEto which the disclosure is applied.

FIG. 4B is a block diagram illustrating the configuration of a basestation according to the disclosure.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. In addition, in thedescription of the present invention, if it is determined that adetailed description of a related known function or configuration mayunnecessarily obscure the gist of the present invention, the detaileddescription thereof will be omitted. In addition, the terms to bedescribed later are terms defined in consideration of functions in thepresent invention, which may vary according to intentions or customs ofusers and operators. Therefore, the definition should be made based onthe content throughout this specification.

The terms used, in the following description, for indicating accessnodes, network entities, messages, interfaces between network entities,and diverse identity information is provided for convenience ofexplanation. Accordingly, the terms used in the following descriptionare not limited to specific meanings but may be replaced by other termsequivalent in technical meanings.

In the following descriptions, the terms and definitions given in the3GPP standards are used for convenience of explanation. However, thepresent disclosure is not limited by use of these terms and definitionsand other arbitrary terms and definitions may be employed instead.

Table 1 lists the acronyms used throughout the present disclosure.

TABLE 1 Acronym Full name 5GC 5G Core Network ACK Acknowledgement AMAcknowledged Mode AMF Access and Mobility Management Function ARQAutomatic Repeat Request AS Access Stratum ASN.1 Abstract SyntaxNotation One BSR Buffer Status Report BWP Bandwidth Part CA CarrierAggregation CAG Closed Access Group CG Cell Group C-RNTI Cell RNTI CSIChannel State Information DCI Downlink Control Information DRB (user)Data Radio Bearer DRX Discontinuous Reception HARQ Hybrid AutomaticRepeat Request IE Information element LCG Logical Channel Group MACMedium Access Control MIB Master Information Block NAS Non-AccessStratum NG-RAN NG Radio Access Network NR NR Radio Access PBRPrioritised Bit Rate PCell Primary Cell PCI Physical Cell IdentifierPDCCH Physical Downlink Control Channel PDCP Packet Data ConvergenceProtocol PDSCH Physical Downlink Shared Channel PDU Protocol Data UnitPHR Power Headroom Report PLMN Public Land Mobile Network PRACH PhysicalRandom Access Channel PRB Physical Resource Block PSS PrimarySynchronisation Signal PUCCH Physical Uplink Control Channel PUSCHPhysical Uplink Shared Channel RACH Random Access Channel RAN RadioAccess Network RA-RNTI Random Access RNTI RAT Radio Access Technology RBRadio Bearer RLC Radio Link Control RNA RAN-based Notification Area RNAURAN-based Notification Area Update RNTI Radio Network TemporaryIdentifier RRC Radio Resource Control RRM Radio Resource Management RSRPReference Signal Received Power RSRQ Reference Signal Received QualityRSSI Received Signal Strength Indicator SCell Secondary Cell SCSSubcarrier Spacing SDAP Service Data Adaptation Protocol SDU ServiceData Unit SFN System Frame Number S-GW Serving Gateway SI SystemInformation SIB System Information Block SpCell Special Cell SRBSignalling Radio Bearer SRS Sounding Reference Signal SSB SS/PBCH blockSSS Secondary Synchronisation Signal SUL Supplementary Uplink TMTransparent Mode UCI Uplink Control Information UE User Equipment UMUnacknowledged Mode

Table 2 lists the terminologies and their definition used throughout thepresent disclosure.

TABLE 2 Terminology Definition allowedCG-List List of configured grantsfor the corresponding logical channel. This restriction applies onlywhen the UL grant is a configured grant. If present, UL MAC SDUs fromthis logical channel can only be mapped to the indicated configuredgrant configuration. If the size of the sequence is zero, then UL MACSDUs from this logical channel cannot be mapped to any configured grantconfigurations. If the field is not present, UL MAC SDUs from thislogical channel can be mapped to any configured grant configurations.allowedSCS-List List of allowed sub-carrier spacings for thecorresponding logical channel. If present, UL MAC SDUs from this logicalchannel can only be mapped to the indicated numerology. Otherwise, ULMAC SDUs from this logical channel can be mapped to any configurednumerology. allowedServingCells List of allowed serving cells for thecorresponding logical channel. If present, UL MAC SDUs from this logicalchannel can only be mapped to the serving cells indicated in this list.Otherwise, UL MAC SDUs from this logical channel can be mapped to anyconfigured serving cell of this cell group. Carrier center frequency ofthe cell. frequency Cell combination of downlink and optionally uplinkresources. The linking between the carrier frequency of the downlinkresources and the carrier frequency of the uplink resources is indicatedin the system information transmitted on the downlink resources. CellGroup in dual connectivity, a group of serving cells associated witheither the MeNB or the SeNB. Cell reselection A process to find a bettersuitable cell than the current serving cell based on the systeminformation received in the current serving cell Cell selection Aprocess to find a suitable cell either blindly or based on the storedinformation Dedicated Signalling sent on DCCH logical channel betweenthe network and a single UE. signalling discardTimer Timer to controlthe discard of a PDCP SDU. Starting when the SDU arrives. Upon expiry,the SDU is discarded. F The Format field in MAC subheader indicates thesize of the Length field. Field The individual contents of aninformation element are referred to as fields. Frequency set of cellswith the same carrier frequency. layer Global cell An identity touniquely identifying an NR cell. It is consisted of cellIdentity andidentity plmn-Identity of the first PLMN-Identity in plmn-IdentityListin SIB1. gNB node providing NR user plane and control plane protocolterminations towards the UE, and connected via the NG interface to the5GC. Handover procedure that changes the serving cell of a UE inRRC_CONNECTED. Information A structural element containing single ormultiple fields is referred as element information element. L The Lengthfield in MAC subheader indicates the length of the corresponding MAC SDUor of the corresponding MAC CE LCID 6 bit logical channel identity inMAC subheader to denote which logical channel traffic or which MAC CE isincluded in the MAC subPDU MAC-I Message Authentication Code -Integrity. 16 bit or 32 bit bit string calculated by NR IntegrityAlgorithm based on the security key and various fresh inputs Logical alogical path between a RLC entity and a MAC entity. There are multiplechannel logical channel types depending on what type of information istransferred e.g. CCCH (Common Control Channel), DCCH (Dedicate ControlChannel), DTCH (Dedicate Traffic Channel), PCCH (Paging Control Channel)LogicalChannelConfig The IE LogicalChannelConfig is used to configurethe logical channel parameters. It includes priority,prioritisedBitRate, allowedServingCells, allowedSCS-List,maxPUSCH-Duration, logicalChannelGroup, allowedCG- List etclogicalChannelGroup ID of the logical channel group, as specified in TS38.321, which the logical channel belongs to MAC CE Control Elementgenerated by a MAC entity. Multiple types of MAC CEs are defined, eachof which is indicated by corresponding LCID. A MAC CE and acorresponding MAC sub-header comprises MAC subPDU Master Cell in MR-DC,a group of serving cells associated with the Master Node, Groupcomprising of the SpCell (PCell) and optionally one or more SCells.maxPUSCH-Duration Restriction on PUSCH-duration for the correspondinglogical channel. If present, UL MAC SDUs from this logical channel canonly be transmitted using uplink grants that result in a PUSCH durationshorter than or equal to the duration indicated by this field.Otherwise, UL MAC SDUs from this logical channel can be transmittedusing an uplink grant resulting in any PUSCH duration. NR NR radioaccess PCell SpCell of a master cell group. PDCP entity The processtriggered upon upper layer request. It includes the initialization ofreestablishment state variables, reset of header compression andmanipulating of stored PDCP SDUs and PDCP PDUs. The details can be foundin 5.1.2 of 38.323 PDCP suspend The process triggered upon upper layerrequest. When triggered, transmitting PDCP entity set TX_NEXT to theinitial value and discard all stored PDCP PDUs. The receiving entitystop and reset t-Reordering, deliver all stored PDCP SDUs to the upperlayer and set RX_NEXT and RX_DELIV to the initial value PDCP-config TheIE PDCP-Config is used to set the configurable PDCP parameters forsignalling and data radio bearers. For a data radio bearer,discardTimer, pdcp-SN-Size, header compression parameters, t-Reorderingand whether integrity protection is enabled are configured. For asignaling radio bearer, t-Reordering can be configured PLMN ID Check theprocess that checks whether a PLMN ID is the RPLMN identity or an EPLMNidentity of the UE. Primary Cell The MCG cell, operating on the primaryfrequency, in which the UE either performs the initial connectionestablishment procedure or initiates the connection re-establishmentprocedure. Primary SCG Cell For dual connectivity operation, the SCGcell in which the UE performs random access when performing theReconfiguration with Sync procedure. priority Logical channel priority,as specified in TS 38.321. an integer between 0 and 7. 0 means thehighest priority and 7 means the lowest priority PUCCH SCell a SecondaryCell configured with PUCCH. Radio Bearer Logical path between a PDCPentity and upper layer (i.e. SDAP entity or RRC) RLC bearer RLC and MAClogical channel configuration of a radio bearer in one cell group. RLCbearer The lower layer part of the radio bearer configuration comprisingthe RLC and configuration logical channel configurations. RX_DELIV Thisstate variable indicates the COUNT value of the first PDCP SDU notdelivered to the upper layers, but still waited for. RX_NEXT This statevariable indicates the COUNT value of the next PDCP SDU expected to bereceived. RX_REORD This state variable indicates the COUNT valuefollowing the COUNT value associated with the PDCP Data PDU whichtriggered t-Reordering. Serving Cell For a UE in RRC_CONNECTED notconfigured with CA/DC there is only one serving cell comprising of theprimary cell. For a UE in RRC_CONNECTED configured with CA/DC the term‘serving cells’ is used to denote the set of cells comprising of theSpecial Cell(s) and all secondary cells. SpCell primary cell of a masteror secondary cell group. Special Cell For Dual Connectivity operationthe term Special Cell refers to the PCell of the MCG or the PSCell ofthe SCG, otherwise the term Special Cell refers to the PCell. SRBSignalling Radio Bearers” (SRBs) are defined as Radio Bearers (RBs) thatare used only for the transmission of RRC and NAS messages. SRB0 SRB0 isfor RRC messages using the CCCH logical channel SRB1 SRB1 is for RRCmessages (which may include a piggybacked NAS message) as well as forNAS messages prior to the establishment of SRB2, all using DCCH logicalchannel; SRB2 SRB2 is for NAS messages and for RRC messages whichinclude logged measurement information, all using DCCH logical channel.SRB2 has a lower priority than SRB1 and may be configured by the networkafter AS security activation; SRB3 SRB3 is for specific RRC messageswhen UE is in (NG)EN-DC or NR-DC, all using DCCH logical channel SRB4SRB4 is for RRC messages which include application layer measurementreporting information, all using DCCH logical channel. Suitable cell Acell on which a UE may camp. Following criteria apply The cell is partof either the selected PLMN or the registered PLMN or PLMN of theEquivalent PLMN list The cell is not barred The cell is part of at leastone TA that is not part of the list of “Forbidden Tracking Areas forRoaming” (TS 22.011 [18]), which belongs to a PLMN that fulfils thefirst bullet above. The cell selection criterion S is fulfilled (i.e.RSRP and RSRQ are better than specific values t-Reordering Timer tocontrol the reordering operation of received PDCP packets. Upon expiry,PDCP packets are processed and delivered to the upper layers. TX_NEXTThis state variable indicates the COUNT value of the next PDCP SDU to betransmitted. UE Inactive UE Inactive AS Context is stored when theconnection is suspended and AS Context restored when the connection isresumed. It includes information below. the current KgNB and KRRCintkeys, the ROHC state, the stored QoS flow to DRB mapping rules, theC-RNTI used in the source PCell, the cellIdentity and the physical cellidentity of the source PCell, the spCellConfigCommon withinReconfigurationWithSync of the NR PSCell (if configured) and all otherparameters configured except for: parameters withinReconfigurationWithSync of the PCell; parameters withinReconfigurationWithSync of the NR PSCell, if configured; parameterswithin MobilityControlInfoSCG of the E-UTRA PSCell, if configured;servingCellConfigCommonSIB;

In the present invention, “trigger” or “triggered” and “initiate” or“initiated” may be used in the same meaning.

In the present invention, “radio bearers allowed for the second resumeprocedure”, “radio bearers for which the second resume procedure isset”, and “radio bearers for which the second resume procedure isenabled” may all have the same meaning.

FIG. 1A is a diagram illustrating the architecture of an 5G system and aNG-RAN to which the disclosure may be applied. 5G system consists ofNG-RAN 1 a-01 and 5GC 1 a-02. An NG-RAN node is either:

-   -   A gNB, providing NR user plane and control plane protocol        terminations towards the UE; or    -   An ng-eNB, providing E-UTRA user plane and control plane        protocol terminations towards the UE.

The gNBs 1 a-05 or 1 a-06 and ng-eNBs 1 a-03 or 1 a-04 areinterconnected with each other by means of the Xn interface. The gNBsand ng-eNBs are also connected by means of the NG interfaces to the 5GC,more specifically to the AMF (Access and Mobility Management Function)and to the UPF (User Plane Function). AMF 1 a-07 and UPF 1 a-08 may berealized as a physical node or as separate physical nodes.

A gNB 1 a-05 or 1 a-06 or an ng-eNBs 1 a-03 or 1 a-04 hosts thefunctions listed below.

Functions for Radio Resource Management such as Radio Bearer Control,Radio Admission Control, Connection Mobility Control, Dynamic allocationof resources to UEs in uplink, downlink and sidelink(scheduling); and

IP and Ethernet header compression, uplink data decompression andencryption of user data stream; and

Selection of an AMF at UE attachment when no routing to an MME can bedetermined from the information provided by the UE; and

Routing of User Plane data towards UPF; and

Scheduling and transmission of paging messages; and

Scheduling and transmission of broadcast information (originated fromthe AMF or O&M); and

Measurement and measurement reporting configuration for mobility andscheduling; and

Session Management; and

QoS Flow management and mapping to data radio bearers; and

Support of UEs in RRC_INACTIVE state; and

Radio access network sharing; and

Tight interworking between NR and E-UTRA; and

Support of Network Slicing.

The AMF 1 a-07 hosts the functions such as NAS signaling, NAS signalingsecurity, AS security control, SMF selection, Authentication, Mobilitymanagement and positioning management.

The UPF 1 a-08 hosts the functions such as packet routing andforwarding, transport level packet marking in the uplink, QoS handlingand the downlink, mobility anchoring for mobility etc.

FIG. 1B is a diagram illustrating a wireless protocol architecture in an5G system to which the disclosure may be applied.

User plane protocol stack consists of SDAP 1 b-01 or 1 b-02, PDCP 1 b-03or 1 b-04, RLC 1 b-05 or 1 b-06, MAC 1 b-07 or 1 b-08 and PHY 1 b-09 or1 b-10. Control plane protocol stack consists of NAS 1 b-11 or 1 b-11b-, RRC 1 b-13 or 1 b-14, PDCP, RLC, MAC and PHY.

Each protocol sublayer performs functions related to the operationslisted in the Table 3.

TABLE 3 Sublayer Functions NAS authentication, mobility management,security control etc RRC System Information, Paging, Establishment,maintenance and release of an RRC connection, Security functions,Establishment, configuration, maintenance and release of SignallingRadio Bearers (SRBs) and Data Radio Bearers (DRBs), Mobility, QoSmanagement, Detection of and recovery from radio link failure, NASmessage transfer etc. SDAP Mapping between a QoS flow and a data radiobearer, Marking QoS flow ID (QFI) in both DL and UL packets. PDCPTransfer of data, Header compression and decompression, Ciphering anddeciphering, Integrity protection and integrity verification,Duplication, Reordering and in-order delivery, Out-of-order deliveryetc. RLC Transfer of upper layer PDUs, Error Correction through ARQ,Segmentation and re-segmentation of RLC SDUs, Reassembly of SDU, RLCre-establishment etc. MAC Mapping between logical channels and transportchannels, Multiplexing/demultiplexing of MAC SDUs belonging to one ordifferent logical channels into/from transport blocks (TB) deliveredto/from the physical layer on transport channels, Scheduling informationreporting, Priority handling between UEs, Priority handling betweenlogical channels of one UE etc. PHY Channel coding, Physical-layerhybrid-ARQ processing, Rate matching, Scrambling, Modulation, Layermapping, Downlink Control Information, Uplink Control Information etc.

The terminal supports three RRC states. Table 4 lists thecharacteristics of each state.

TABLE 4 RRC state Characteristic RRC_IDLE PLMN selection; Broadcast ofsystem information; Cell re-selection mobility; Paging for mobileterminated data is initiated by 5GC; DRX for CN paging configured byNAS. RRC_INACTIVE PLMN selection; Broadcast of system information; Cellre-selection mobility; Paging is initiated by NG-RAN (RAN paging);RAN-based notification area (RNA) is managed by NG-RAN; DRX for RANpaging configured by NG-RAN; 5GC - NG-RAN connection (both C/U-planes)is established for UE; The UE AS context is stored in NG-RAN and the UE;NG-RAN knows the RNA which the UE belongs to. RRC_CONNECTED 5GC - NG-RANconnection (both C/U-planes) is established for UE; The UE AS context isstored in NG-RAN and the UE; NG-RAN knows the cell which the UE belongsto; Transfer of unicast data to/from the UE; Network controlled mobilityincluding measurements.

FIG. 1C is a diagram illustrating an RRC state transition.

Between RRC_CONNECTED 1 c-11 and RRC_INACTIVE 1 c-13, a state transitionoccurs due to the exchange of the Resume message and the Release messagecontaining the Suspend IE.

A state transition occurs between RRC_CONNECTED 1 c-11 and RRC_IDLE 1c-15 through RRC connection establishment and RRC connection release.

The state transition from RRC_INACTIVE to RRC_CONNECTED involves notonly signal exchange between the terminal and the base station, but alsocontext transfer and data path change between the base stations. If theterminal has enough data to transmit, these additional procedures can besufficiently justified, but if not, excessive overhead can reduce theefficiency of the network.

The present invention introduces a new resumption procedure capable oftransmitting and receiving data without transition to RRC_CONNECTED.Hereinafter, a resume procedure for the purpose of transitioning theterminal to the RRC_CONNECTED state from the RRC_INACTIVE state isreferred as to a first resume procedure, and a procedure fortransmitting and receiving data while the terminal is in theRRC_INACTIVE state is referred to as a second resume procedure. Throughthe first resume procedure, the terminal may resume the suspended RRCconnection, and through the second resume procedure, the terminal mayresume data transmission and reception. The terminal may switch to thefirst resume procedure while performing the second resume procedure.

FIG. 2A is a diagram illustrating operations of a terminal and a basestation according to an embodiment of the present invention.

In a wireless communication system including a terminal 2 a-01, a firstbase station 2 a-03, and a second base station 2 a-05, the terminal andthe base station operate as follows.

In steps 2 a-11, the terminal reports capability to the first basestation or another base station. The UE capability information transferprocedure consists of transmitting an RRC control message calledUECapabilityInformation containing UE capability information to theserving base station if the serving base station transmits an RRCmessage requesting UE capability information. UECapabilityInformationincludes the following information.

<UECapabilityInformation>

1. First information related to RRC_INACTIVE: 1-bit informationindicating whether the terminal supports RRC_INACTIVE. Only one 1-bit isreported regardless of the number of bands supported by the terminal.

2. Second information related to RRC_INACTIVE: information indicatingwhether the second resume procedure is supported or not. It may indicatewhether the second resume procedure is supported for each band supportedby the terminal. When the terminal supports n bands, n 1-bit informationis reported.

3. Various pieces of capability information related to datatransmission/reception between the terminal and the base station (forexample, whether specific decoding is supported, etc.).

The terminal supporting RRC_INACTIVE supports the first resume procedurein all frequency bands supported by the terminal. That is, the firstinformation related to RRC_INACTIVE support is information applied to aplurality of bands, and the second information related to RRC_INACTIVEis information applied to one band. A terminal that does not supportRRC_INACTIVE does not support the second resume procedure in anyfrequency band that it supports. The serving base station providesappropriate NR configuration information to the UE by referring to thecapability of the UE. The UE and the serving base station transmit andreceive data in the RRC_CONNECTED state, and when the data transmissionand reception are completed, the serving base station determines totransition the terminal state to the RRC_INACTIVE state.

In step 2 a-13, the first base station transmits an RRCRelease messageto the terminal. The RRCRelease message includes SuspendConfig IE, andSuspendConfig includes the following information.

<SuspendConfig>

1. The first terminal identifier: an identifier of a terminal that maybe included in the ResumeRequest when a state transition toRRC_CONNECTED is made. It has a 40-bit length.

2. The second terminal identifier: an identifier of a terminal that maybe included in the Resume Request when a state transition toRRC_CONNECTED is made. It has a 24-bit length.

3. ran-Paging Cycle: Paging cycle to be applied in RRC_INACTIVE state.

4. ran-Notification AreaInfo: Configuration information of aran-Notification Area consisting of a list of cells and the like. Theterminal initiates a resume procedure when the ran_Notification Area ischanged.

5. t380: Timer related to the periodic resumption procedure.

6. NextHopChangingCount (NCC): Counter used to derive new security keysafter performing the resume procedure.

7. Second resume procedure related information: List of DRBs configuredwith second resume procedures, 1-bit information indicating whether thesecond resume procedure is configured for SRB2, 1-bit informationindicating whether the second resume procedure is configured for SRB4,Data size threshold of the second resume procedure (hereinafter referredto as dedicated data threshold), reference signal received powerthreshold of the second resume procedure (hereinafter referred to asdedicated reference signal received power threshold)

Since SRB1 among SRB1, SRB2, SRB3, and SRB4 transmits and receives themost important RRC control message, it is important to quickly transmitthe RRC control message as the second resume procedure, and the secondresume procedure is highly effective for SRB1. SRB2 and SRB4 are lessimportant than SRB1 because relatively large messages can occur, butthey still transmit important control messages, so the second resumeprocedure is effective for SRB2 and SRB4. SRB3 is not used when multipleconnections are not established. Accordingly, in the present invention,a second resume procedure can be explicitly configured for SRB2 andSRB4. A second resume procedure is not explicitly configured for SRB1and SRB3. If a second resume procedure is configured for at least oneradio bearer, a second resume procedure is implicitly configured forSRB1. A second resume procedure is not configured for SRB3 under anyconditions.

In step 2 a-14, the terminal performs the SuspendConfig operation set.The SuspendConfig operation set is applied at a predetermined first orsecond time point. For the SuspendConfig operation set is performed, thefollowing operations are sequentially performed.

<SuspendConfig Operation Set>

1. Apply suspendConfig.

2. Reset MAC.

3. Reset SRB1's RLC entity.

4. All SRBs and DRBs are suspended.

5. Start T380 set to t380.

6. Enter RRC_INACTIVE state.

The terminal applies the first time point for SuspendConfig operationset when the second resume related information is included, and thesecond time point if not included.

The first time point is as follows.

Earlier time point between a time point at which 100 ms has elapsedsince receiving the RRCRelease message and a time point at which thelower layer successfully acknowledged the reception of the RRCReleasemessage.

The second time point is as follows.

Earlier time point between a time point at which 60 ms has elapsed sincereceiving the RRCRelease message and a time point at which the lowerlayer successfully acknowledged the reception of the RRCRelease message.

Different time points are used because the reliability of the RRCRelease message including the second resume-related information shouldbe higher than that of the RRC Release message not including the secondresume information.

In step 2 a-15, the terminal moves to a new cell. The terminal maycompare the radio signal quality of the serving cell and the neighboringcell to reselect the neighboring cell having a better radio signalquality. Alternatively, a cell in which the radio signal quality isgreater than or equal to a certain threshold may be selected.

In steps 2 a-17, the terminal receives system information including SIB1in a new cell. The SIB1 may include at least two types of informationbelow.

<SIB1>

1. The value of t319

2. 1-bit information indicating whether the second resume procedure isallowed (or whether the second resume procedure is configured orpossible).

If the second resume procedure is allowed, the following information isincluded and broadcast in system information (hereinafter, SIBX) otherthan SIB1.

<SIBX>

1. Data size threshold of the second resume procedure (hereinafter,referred to as public data threshold)

2. Reference signal received power threshold of the second resumeprocedure (hereinafter, referred to as a common reference signalreceived power threshold)

3. Random access transmission resource information for the second resumeprocedure.

4. t319ext

The terminal receives the SIBX if there is at least one radio bearerconfigured with a second resume procedure, i.e., if the second resumeprocedure is configured for at least one DRB or if the second resumeprocedure is configured for SRB2 or SRB4.

The terminal receiving the necessary system information including SIB1performs the RRC_INACTIVE operation shown in Table 4 in the cell.

In step 2 a-19, an event that triggers the resume procedure occurs. Whenthe upper layer or AS requests the resumption of the suspended RRCconnection or when new data occurs, the resume procedure may betriggered.

In step 2 a-21, the terminal triggers one of the first resume procedureand the second resume procedure. If any condition of the first resumecondition group is satisfied, the first resume procedure is triggered.

<First Resume Condition Group>

1. The upper layer requests the resumption of the suspended RRCconnection.

2. RAN paging including the first identifier is received.

3. RNA update occurs.

4. Data has been generated in the radio bearer that is allowed totrigger the second resume procedure, but at least one of the secondresume condition group is not satisfied.

If all conditions of the second resume condition group are satisfied,the second resume procedure is triggered.

<Second Resume Condition Group>

1. Data available for transmission is generated in a bearer belonging tothe first bearer set.

2. The amount of data available for transmission from the bearerbelonging to the first bearer set is less than the final data threshold.

3. The reference signal received power of the current serving cell ishigher than the final reference signal received power threshold.

4. The current serving cell provides transmission resource for thesecond resume procedure.

A radio bearer that triggering second resume procedure is allowed (or asecond resume procedure is allowed) means DRB that a second resumeprocedure is allowed and SRB a second resume procedure is allowed. Thesecond resume procedure is not allowed for SRB3, and SRB2 and SRB4 areindicated by explicit information whether the second resume procedure isallowed. When the second resume procedure is allowed in at least oneradio bearer, the second resume procedure is automatically allowed inthe SRB1.

The final data threshold is the lower of the dedicated data thresholdand the common data threshold or alternatively the dedicated datathreshold, if there are both dedicated data thresholds and common datathresholds. If there is only one, it is the final data threshold.Alternatively, if there are both dedicated data thresholds and commondata thresholds, the common data threshold is the final data threshold,and if there is only one, it is the final data threshold.

The final reference signal received power threshold is a higher of thededicated reference signal received power threshold and the commonreference signal received power threshold or the dedicated referencesignal received power threshold, if there are both dedicated referencesignal received power threshold and common reference signal receivedpower threshold. If there is only one, it is the final data threshold.Or, if there are both dedicated reference signal received powerthreshold and common reference signal received power threshold, thecommon reference signal received power threshold is the final referencesignal received power threshold, and if there is only one, it is thefinal data threshold.

When at least one of the first condition group is satisfied and all ofthe second condition group are satisfied, that is, when both the firstresume procedure and the second resume procedure are triggered, theterminal selects the second resume procedure.

In step 2 a-23, the terminal performs a first resume procedure or asecond resume procedure with the base station.

FIG. 2B is a diagram illustrating a first resume procedure and a secondresume procedure according to an embodiment of the present invention.

The first resume procedure is as follows.

In step 2 b-11, the terminal performs the first resume operation set 1.The first resume operation set 1 is operations taken when the firstresume procedure is started, and as follows. By performing the firstoperation set 1, the terminal may receive a downlink control messagefrom the base station via SRB1.

<First Resume Operation Set 1>

1. Apply default SRB1 configuration.

2. Apply default MAC Cell Group configuration

3. Start T319 set to t319 received from SIB1.

The default SRB1 configuration is as follows.

TABLE 5 Value Name SRB1 SRB2 SRB3 PDCP-Config >t-Reordering infinityRLC-Config CHOICE Am ul-AM-RLC >sn-FieldLength size12 >t-PollRetransmitms 45 >pollPDU infinity >pollByte infinity >maxRetxThreshold t8dl-AM-RLC>sn-FieldLength size12 >t-Reassembly ms 35 >t-StatusProhibit ms0  logicalChannelIdentity 1 2 3 LogicalChannelConfig >priority 1 31 >prioritisedBitRate infinity >logicalChannelGroup 0

The default MAC Cell Group configuration is as follows.

TABLE 6 Name Value MAC Cell Group configurationbsr-Config >periodicBSR-Timer sf10 >retxBSR-Timer sf80phr-Config >phr-PeriodicTimer sf10 >phr-ProhibitTimersf10 >phr-Tx-PowerFactorChange dB1

T319 set to t319 is a timer to perform follow-up measures, for example,transition to RRC_IDLE, etc., when the first resume procedure fails.T319 set to t319 is stopped when RRCResume is received. If the RRCResumeis not received until the T319 set to t319 expires, the terminalperforms the T319 expiration operation set.

<T319 Expiration Operation Set>

1. Reset MAC.

2. Discard UE Inactive AS Context.

3. Release suspendConfig.

4. Discard the security key.

5. Release all RLC entities, PDCP entities, and SDAP entities.

6. Transition to RRC_IDLE and perform cell selection operation.

In step 2 b-13, the terminal performs the first resume procedureoperation set 2. The first resume procedure operation set 2 isoperations taken before transmitting the ResumeRequest.

<First Resume Procedure Operation Set 2>

0. Restore RRC configurations of UE Inactive AS context exceptmasterCellGroup and PDCP-config.

1. ResumeMAC-I calculation: Calculate a 16-bit message verification codeusing the first security key (a security key used in the RRC_CONNECTEDstate or a security key used at the time of receiving RRC Release).

2. Deriving the second base station security key using the second basestation security key. From the second base station security key, thesecond security key, the third security key, the fourth security key,and the fifth security key are derived.

3. All radio bearers except SRB0 are configured to use second securitykey and third security key or fourth security key and fifth securitykey.

3. Reset the PDCP entity of SRB 1.

4. Resume SRB1.

In step 2 b-15, the terminal transmits a ResumeRequest message to thesecond base station. The MAC PDU containing the ResumeRequest messagedoes not include data from other radio bearers. ResumeRequest includesthe information below.

<ResumeRequest>

1. The first identifier or the second identifier: an identifierindicated in the system information among the first and secondidentifiers given in SuspendConfig is included.

2. ResumeMAC-I: 16-bit message verification code to ensure integrity ofthe resume request message. The terminal calculates the resume MAC-Iusing the previous security key (a security key used in theRRC_CONNECTED state or a security key used at the time of receiving theRRC Release).

3. resumeCause: Indicating one of emergency, highPriorityAccess,mt-Access, mo-Signalling, mo-Data, mo-VoiceCall, mo-VideoCall, mo-SMS,rna-Update, mps-PriorityAccess, mcs-PriorityAccess and smallDataTransferThe terminal performing the first resume procedure selects one of theremaining values except for smallDataTransfer as the resumeCause. Thisis to enable the base station to determine whether the second resumeprocedure is performed through the resumeCause.

In step 2 b-17, the terminal receives the RRC Resume. RRCResume includesthe following information.

<RRCResume>

1. MasterCellGroup: CellGroupConfig for masterCellGroup includes RLCbearer information, MAC configuration information, PHY configurationinformation, and SpCell configuration information.

2. RadioBearrConfig: It is radio bearer configuration information andincludes SRB configuration information and DRB configurationinformation.

In step 2 b-19, the terminal performs the first resume procedureoperation set 3.

<First Resume Procedure Operation Set 3>

1. Stop T319.

2: Stop T380.

3: Restore and apply masterCellGroup of UE Inactive AS Context

4: Apply CellGroupConfig and radioBearerConfig in RRCResume

5. Resume SRB2, SRB3, and all DRBs.

6. Transition to RRC_CONNECTED state.

7. Stop cell reselection procedure.

In step 2 b-21, the terminal transmits an RRCResumeComplete message tothe second base station. The RRCResumeComplete message includes PLMNidentifier information selected by the terminal.

In step 2 b-23, the terminal and the second base station transmit andreceive data. In this case, the terminal may transmit a MAC CE such asBSR or PHR to the base station together. When the BSR trigger conditionis satisfied, the terminal multiplexes the BSR in the uplink MAC PDU andtransmit the MAC PDU. When the PHR trigger condition is satisfied, theterminal multiplexes the PHR MAC CE in the uplink MAC PDU and transmitthe MAC PDU. BSR trigger conditions include arrival of new data withhigh priority and expiration of periodic timers. PHR trigger conditionsinclude change of reference signal received power more than a predefinedthreshold, activation of a new secondary cell, and the like.

In step 2 b-25, when data transmission/reception with the terminal iscompleted, the second base station transmits an RRC Release includingSuspendConfig to the terminal to transition the terminal to theRRC_INACTIVE state.

In step 2 b-27, the terminal receiving the RRCRelease message includingSuspendConfig starts T380.

The second resume procedure is as follows.

In steps 2 b-31, the terminal performs the second resume operationset 1. The second resume operation set 1 is operations taken when thesecond resume procedure is triggered as follows. By performing thesecond resume operation set 1, the terminal may receive a downlinkcontrol message from the base station via the SRB1 and transmit uplinkdata of the radio bearer (or data transmission in the INACTIVE state, orin which the second resume procedure is configured).

<Second Resume Operation Set 1>

0: Restore all RRC configuration of UE Inactive AS Context (includingradio bearer settings of the first set of bearers, masterCellGroup, andPDCP-config).

1. start T319ext set to t319ext

2. stop T380

3. ResumeMAC-I calculation: A 16-bit MAC-I is calculated using theprevious K_RRCint, that is, the first security key (K_RRCint used in theprevious RRC_CONNECTED state or K_RRCint used at the time of receivingRRCRelease).

4. Deriving the second base station security key using the first basestation security key and the NCC. From the second base station securitykey, the second security key, the third security key, the fourthsecurity key, and the fifth security key are derived.

5. Configure the first bearer set to apply the second security key andthe third security key or the fourth security key and the fifth securitykey.

6. Reset the PDCP entity of the first bearer set.

7. Resume the radio bearer of the first bearer set.

8. Stop cell reselection procedure

9. Start the second cell reselection procedure.

T319ext set to t319ext is a timer to perform follow-up measures, forexample, transition to RRC_IDLE, etc., when the second resume procedurefails. T319, T319ext, and T380 have the following characteristics.

TABLE 7 First reconfiguration T380 T319 Configured by RRCRelease SIB1Start Upon reception of RRCRelease After start of first reconfigurationprocedure, between the time point when configuration received from SIB1is applied and the time point when SRB1 resumes Stop Upon reception ofRRCResume Upon reception of RRCResume and before applying cell group andbefore applying cell group configuration configuration Upon expirationInitiating periodic RNA update in T319 expiry operation set the currentcell Second reconfiguration T380 T319ext Configured by RRCRelease SIB XStart Upon reception of RRCRelease After start of second reconfigurationprocedure, between the time point when SRB1 configuration stored in UEInactive AS Context is applied and the time point when SRB1 resumes StopAfter start of second Upon reception of RRCRelease or reconfigurationprocedure, before applying cell group between the time point whenconfiguration SRB1 configuration stored in UE Inactive AS Context isapplied and the time point when SRB1 resumes Upon expiration Determiningwhether to initiate T319ext expiry operation set periodic RNA update inthe current cell

In the first resume procedure, T380 and T319 stops before configuringcell group information after receiving the RRCResume message to preventunnecessary subsequent operation due to the timer expiration by stoppingthe timers as a first operation after receiving the RRCResume message.

In the first resume procedure, starting T319 between the time point whenthe default SRB1 configuration is applied and the time point when SRB1resumes is to start T319 as close as possible to the time point whenSRB1 becomes available.

In the second resume procedure, starting T319ext between the time pointwhen SRB1 configuration stored in UE Inactive AS Context is applied andthe time point when SRB1 resumes is to start T319ext as close aspossible to the time point when SRB1 becomes available.

In the second resume procedure, starting T380 between the time pointwhen SRB1 configuration stored in UE Inactive AS Context is applied andthe time point when SRB1 resumes is to start T380 as close as possibleto the time point when T319ext starts so that the processing load fortimer handling in UE is reduced.

The time point when SRB1 configuration stored in UE Inactive AS Contextis applied and the time point when radio bearer configuration for firstbearer set stored in UE Inactive AS Context is applied are same.

If the RRCResume is not received until the T319ext set to t319extexpires, the terminal may perform the T319ext expiration operation setor the T319 expiration operation set. The base station may set inSuspendConfig or in system information which one to select between theT319ext expiration operation set and the T319 expiration operation set.

<T319ext Expiration Operation Set>

1. Reset MAC

2. Keep UE Inactive AS Context

3. Keep suspendConfig

4. Discard first base station security key and first security key in UEand store second base station security key and third security key

5. Suspend all SRBs and DRBs

6. Start T380 set to t380

7. Stop second cell reselection procedure

8. Start cell reselection procedure

9. Perform RNA update after selecting a suitable cell

The first bearer set is a set of radio bearers for which the secondresume procedure is explicitly or implicitly configured and consists ofSRB1 and radio bearers related to the second resume procedure. The radiobearer related to the second resume procedure refers to a radio bearerin which the second resume procedure is explicitly allowed or a radiobearer in which the second resume procedure is explicitly configured.

Stopping the cell reselection procedure means stopping the existing cellreselection procedure performed before the second resume procedurestarts.

UE preferentially selects, in the existing cell reselection procedure, afrequency to camp on by considering cell reselection priority providedby base station, ranks each cell of the selected frequency byconsidering reference signal received power and various offsets, andreselects a highest ranked cell.

When the second cell reselection procedure starts, the terminal stopsusing the cell reselection priority and offsets indicated by the basestation and uses the following parameters.

<Second Cell Reselection Procedure>

1. Increase the cell reselection priority of the current servingfrequency to the highest priority.

2. Increase the first Qhyst by a predetermined value. Or apply the 2ndQhyst.

When the terminal determines the cell ranking, the current serving cellis weighted by Qhyst. That is, the ranking is determined by adding Qhystto the reference signal received power of the current serving cell. Thefirst Qhyst is included in the SIB2 and broadcasted. The second Qhyst orthe predetermined value is included in the SIBX and broadcasted.

In steps 2 b-33, the terminal transmits a MAC PDU including a first SDUincluding a ResumeRequest message and data of first bearer set (or dataof a bearer in which a second resume procedure is configured) to thesecond base station. The terminal performing the second resume procedureselects smallDataTransfer as ResumeCause. The terminal may include apriority-based BSR MAC CE and a PHR MAC CE in the MAC PDU. If theBSR/PHR inclusion condition is satisfied and the BSR/PHR cancellationcondition is not satisfied, the terminal includes and transmits thepriority-based BSR MAC CE and the PHR MAC CE in the MAC PDU. Theterminal transmits MAC PDUs that do not include the priority-based BSRand PHR when the BSR/PHR cancellation condition is satisfied even if theBSR/PHR inclusion condition is satisfied.

<BSR/PHR Inclusion Condition>

There is more data for transmission after transmission of the MAC PDU(or first uplink MAC PDU of the second resume procedure) includingResumeRequest, or uplink grant (or first uplink grant of the secondresume procedure) for transmission of MAC PDU including ResumeRequestdoes not accommodate all pending data available for transmission.

<BSR/PHR Cancellation Condition>

An uplink grant (or the first uplink grant of the second resumeprocedure) for transmission of MAC PDU including ResumeRequest canaccommodate all pending data available for transmission if at least oneof a triggered BSR and corresponding subheader or a triggered PHR arenot included in the MAC PDU but cannot accommodate all pending dataavailable for transmission if both triggered BSR and correspondingsubheader and triggered PHR and corresponding PHR are included in theMAC PDU.

In steps 2 b-35, the terminal and the base station transmit and receivedata of the first bearer set. Data of the first bearer set is scheduledby C-RNTI, and the terminal monitors a frequency region and a timeinterval, indicated in SIBX, for transmitting and receiving smallamounts of data (or for transmitting and receiving data in the secondresume procedure).

When the data transmission is completed, the base station determines toterminate the second resume procedure.

In steps 2 b-37, the second base station transmits an RRCReleaseincluding SuspendConfig to the terminal to terminate the second resumeprocedure. When receiving an RRCRelease including SuspendConfig, theterminal performs the second resume procedure operation set 2 toterminate the second resume procedure.

<Second Resume Operation Set 2>

1. Stop monitoring frequency region and time interval for small datatransmission indicated in SIBX

2. Reset MAC

3. Update suspendConfig

4. Discard first base station security key and first security key in UEand store second base station security key and third security key

5. Suspend all SRBs and DRBs except SRB0

6. Start T380 set to t380

7. Stop second cell reselection procedure

8. Start cell reselection procedure

FIG. 2C is a diagram illustrating a structure of an uplink MAC PDU usedin a second resume procedure.

The MAC SDU (first SDU) 2 c-15 including the ResumeRequest message islocated at the front of the MAC PDU 2 c-11 and the MAC SDU (second SDU)2 c-19 including the data of the first bearer set (data of the bearerwhere second resume procedure is configured) is located at the rear ofthe MAC PDU. This is to enable the base station receiving the MAC PDU torecognize as quickly as possible that the MAC PDU is a MAC PDU relatedto the second resume procedure. The first SDU includes a part of theMAC-I calculated by the first security key (K_RRCint previously used),and the second SDU includes a MAC-I calculated by the fifth security key(new K_UPenc derived from the second base station security key). The MACsub-header 2 c-13 of the first SDU includes two R bits and an LCIDfield, and the MAC sub-header 2 c-17 of the second SDU includes one Rbit, an F field, an LCID field, and an L field. The LCID field indicateswhich logical channel the corresponding MAC SDU belongs to or which MACCE is the corresponding MAC CE, and the L field indicates how many bytesthe corresponding MAC SDU or MAC CE is. A MAC SDU or MAC CE andcorresponding MAC subheader is referred to as a MAC subPDU. The MAC PDU2 c-11 shown in 2 c includes two MAC subPDUs 2 c-21 and 2 c-23.Hereinafter, a structure of the MAC PDU shown in FIG. 2C is referred toas a MAC PDU structure 1. MAC PDU structure 1 is characterized in that aMAC subPDU including a MAC SDU and having an R/LCID subheader locates infront of a MAC subPDU including a MAC SDU and having R/F/LCID/F. Thisfeature allows the base station to process the ResumeRequest message assoon as possible, as described above.

FIG. 2D is a diagram illustrating a structure of a general uplink MACPDU. Although a MAC PDU including two MAC subPDUs is exemplified, oneMAC PDU may include two or more MAC subPDUs. Hereinafter, a structure ofthe MAC PDU shown in FIG. 2 d is referred to as a MAC PDU structure 2.In MAC PDU structure 2, a MAC subPDU having an R/LCID subheader islocated behind a MAC subPDU including a MAC SDU with an R/F/LCID/Fsubheader. MAC subPDUs with R/LCID subheaders correspond to MAC CE inmost cases, and by placing MAC subPDUs including MAC CE behind MACsubPDUs including MAC SDUs, the terminal can process MAC subPDUsincluding MAC SDUs in advance before receiving uplink grant.

The first SDU 2 c-15 is a first RRC control message received by the basestation. Therefore, the base station and the terminal need to processthe first SDU by applying the same configuration without priorconsultation. On the other hand, the second SDU 2 c-20 may be processedafter the base station processes the first SDU and may be processedafter the base station restores the UE Inactive AS Context. Accordingly,the second SDU may be processed according to the configuration stored inUE Inactive AS Context.

In the present invention, a first configuration is applied to the firstSDU and a second configuration is applied to the second SDU. The firstconfiguration refers to a configuration predetermined in the standard(or a configuration standardized with one value), and the secondconfiguration refers to a configuration stored in the UE Inactive ASContext. Usually, one MAC PDU includes only the MAC SDU to which thefirst configuration is applied or only the MAC SDU to which the secondconfiguration is applied, but in the present invention, the MAC SDU towhich the first configuration is applied and the MAC SDU to which thesecond configuration is applied are transmitted together in a single MACPDU. This is to more quickly transmit the MAC SDU to which the secondconfiguration is applied.

The first configuration and the second configuration may include atleast PDCP configuration, RLC configuration, and logical channelconfiguration. The PDCP configuration of the first configuration is PDCPunused, the RLC configuration of the first configuration is RLCTM, thelogical channel configuration of the first configuration is the highestpriority, LCG ID 0, LCID 0, etc. Alternatively, the first configurationmay be a default SRB1 configuration.

The second configuration of a bearer where the second resume procedureis configured is as follows. The PDCP configuration is the PDCPconfiguration of the corresponding bearer stored in the UE Inactive ASContext, the RLC configuration is the RLC configuration of the RLCbearer associated with the corresponding bearer stored in the UEInactive AS Context (e.g., various timer values), and the logicalchannel configuration is the RLC bearer's logical channel configuration.The terminal applies, to the PDCP configuration and the RLCconfiguration, the configuration stored in the UE Inactive AS Context asit is. The terminal applies, to the logical channel configuration, onlysome of the configurations stored in the UE Inactive AS Context and doesnot apply the rest as if they were not configured. The logical channelconfiguration of the radio bearer belonging to the first bearer setconsists of an LCID, an LCG ID, a priority, and variousrestriction-related configurations. In transmitting data of the firstbearer set during the second resume procedure, the terminal uses storedvalues and processes various restriction-related configurations as ifthey were not configured. Various restriction-related configurationsinclude, for example, allowedServingCells, allowedSCS-List, andmaxPUSCH-Duration. If this restriction-related configuration is notconfigured, the terminal determines that there is no restriction on thecorresponding logical channel in transmitting and receiving data of thelogical channel. The stored restriction-related configuration may beapplied when the first resume procedure is initiated.

When the first SDU 2 c-15 and the second SDU 2 c-19 are multiplexed inone MAC PDU during the second resume procedure, the terminal applies apredefined configuration for the first SDU, that is, PDCP not used, RLCTM, highest priority, LCID0 and LCG ID0. The terminal applies, to thesecond SDU, overall PDCP configuration of the corresponding bearer,overall RLC configuration of the RLC bearer of the corresponding bearerand some of logical channel configuration of the RLC bearer of thecorresponding bearer stored in UE Inactive AS Context and does not applythe rest of logical channel configuration of the RLC bearer of thecorresponding bearer. The applied logical channel configuration may bean LCID, a priority and an LCG ID, and the non-applied logical channelconfiguration may be allowedServingCells, allowedSCS-List,maxPUSCH-Duration, and the like.

The terminal generates SDU1 by applying the first configuration, andgenerates SDU2 by applying the second configuration.

The uplink MAC PDU may include a MAC SDU or a MAC CE. The MAC CEcollectively refers to control information generated and transmitted bya MAC layer such as BSR or PHR. MAC CE may have a fixed size or avariable size. The field L is not used for the MAC subheader of the MACCE having a fixed size. A general MAC SDU has a variable size and an Lfield is used for a corresponding sub header. The MAC subPDU includingthe MAC CE is always located behind the MAC subPDU including the MACSDU. Therefore, in a general uplink MAC PDU in which at least two MACsubPDUs are multiplexed, a MAC subPDU having an L field is located infront and a MAC subPDU having no L field is located in rear. In general,all MAC SDUs included in one uplink MAC PDU are protected by a securitykey derived from the same base station security key.

FIG. 2E is a diagram illustrating a hierarchical structure of securitykeys.

The terminal and the base station perform integrity protection andciphering using security keys derived from the KgNB 2 e-11. Foursub-security keys, K_UPenc 2 e-21, K_UPint 2 e-23, K_RRCenc 2 e-25 andK_RRCint 2 e-27 are derived from KgNB 2 e-21. KgNB derives KgNB* 2 e-33by inputting NCC 2 e-31 or the like during a handover or resumeprocedure, and new sub-security keys are derived from the KgNB*.

In FIG. 2C, the first SDU 2 c-15 is integrity protected by K_RRCintderived from KgNB used in the previous cell, that is, at least a part ofthe MAC-I calculated by the K_RRCint is included in the first SDU andtransmitted together, and the second SDU (2 c-19) is integrity protectedby K_UPint and ciphered by K_UPenc among sub-security keys of KgNB*derived from NCC and KgNB used in the previous cell.

That is, some of the MAC SDUs included in one MAC PDU during the secondresume process are protected by a security key derived from KgNB, andthe other MAC SDU is protected by a security key derived from KgNB*.

MAC SDUs multiplexed in the MAC PDU 2 d-11 of FIG. 2 d are ciphered orintegrity protected by a sub-security key derived from one of KgNB andKgNB*.

KgNB previously used or used at the time of receiving RRCRelease is thefirst base station security key. K_RRCint derived from the first basestation security key is the first security key. KgNB* (or derived fromthe first base station security key and NCC or KgNB derived from thesecond resume procedure operation set 1) is the second base stationsecurity key. K_RRCenc, K_RRCint, K_UPenc and K_UPint derived from thesecond security key are denoted as the second security key, the thirdsecurity key, the fourth security key and fifth security key.

Conventionally, one MAC PDU is ciphered or integrity protected withsecurity keys derived from one base station security key. In the presentinvention, by multiplexing MAC SDUs protected with security keys derivedfrom different base station security keys into one MAC PDU, the MAC SDUsare transmitted more quickly.

FIG. 2 h is a diagram illustrating a MAC-I calculation process andciphering process.

The transmitting end 2 h-01 generates MAC-I and transmits the MAC-I tothe receiving end 2 h-02. The transmitting end generates MAC-I 2 h-23 byinputting the security key 2 h-19, COUNT 2 h-11, message 2 h-13,DIRECTION 2 h-15, and BEARER 2 h-17 into the NIA (NR IntegrityAlgorithm) 2 h-21 and transmits the generated MAC-I 2 h-23 to thereceiving end.

The receiving end also calculates XMAC-I 2 h-25 by inputting thesecurity key 2 h-19, COUNT 2 h-11, message 2 h-13, DIRECTION 2 h-15, andBEARER 2 h-17 into the NR integrity algorithm (NIA) 2 h-21, anddetermines that the received MAC-I is the same. MAC-I and XMAC-I may bethe same only when the same NR integrity algorithm (NIA) 2 h-21, thesame security key 2 h-19, the same COUNT 2 h-11, the same message 2h-13, the same DIRECTION 2 h-15, and the same BEARER 2 h-17 are used atthe transmitting end and receiving ends. MAC-I has a 32-bit size.

MAC-I included in the first SDU 2 c-15 of the uplink MAC PDU 2 c-11 ofthe second resume process is the last 16 bits of MAC-I calculated usinga first security key, a COUNT set to all 0s, a DIRECTION set to 0 and amessage consisting of an identifier of a terminal and an identifier of acell.

The MAC-I included in the second SDU 2 c-19 of the uplink MAC PDU (2c-11) of the second resume process is for a PDCP SDU belonging to thefirst bearer set, and is calculated using a fifth security key, a COUNTof the PDCP SDU, a DIRECTION set to 0, and a DRB identifier, and amessage that is the PDCP SDU.

The transmitting end 2 h-31 processes a simple text to a ciphered blockas follows and transmits the same to the receiving end 2 h-32. Thetransmitting end generates a keystream block 2 h-53 by inputting asecurity key 2 h-49, a COUNT 2 h-41, a BEARER 2 h-43, a DIRECTION 2h-45, and a LENGTH 2 h-47 into the NR Encryption Algorithm (NEA) 2 h-51.The transmitting end generates a ciphered block 2 h-35 by applyingexclusively OR calculation to the generated keystream block with simpletext 2 h-33, and transmits the generated ciphered block to the receivingend. The LENGTH is the length of the simple text.

The receiving end inversely converts the received ciphered block intosimple text using the same input and the same security key.

The second SDU 2 c-19 of the uplink MAC PDU 2 c-11 of the second resumeprocess may include a ciphered PDCP SDU of the first bearer set. ThePDCP SDU is ciphered using a fourth security key, a COUNT of the PDCPSDU, a DIRECTION set to 0, a DRB identifier BEARER, and a PDCP SDUlength LENGTH.

FIG. 2F is a diagram illustrating structures of a first BSR MAC CE and asecond BSR MAC CE, which are BSR based on a logical channel group.

The first BSR MAC CE includes one logical channel group identifier field2 f-01 and one first buffer size field 2 f-03. The logical channel groupidentifier field 2 f-01 has a size of 3 bits and indicates one of thelogical channel group identifiers between 0 and 7. The first buffer sizefield 2 f-03 has a 5-bit size and indicates one of the first buffer sizeindexes between 0 and 31. The first buffer size index 0 means that thereis no data available for transmission in the logical channels belongingto the corresponding logical channel group. The first buffer size index31 means that the sum of data available for transmission of the logicalchannels belonging to the corresponding logical channel group is greaterthan the 30th first buffer size. The first buffer size index 1 meansthat sum of data available for transmission of the logical channelsbelonging to the corresponding logical channel group is greater than 0and less than or equal to the first buffer size. The first buffer sizeindex n (2<=n<=30) indicates that sum of data available for transmissionof the logical channels belonging to the corresponding logical channelgroup is greater than or equal to the n−1th first buffer size and lessthan or equal to the nth first buffer size. The 30 first buffer sizesare defined in the standard.

The second BSR MAC CE includes eight LCGi bits 2 f-11 and a plurality ofsecond buffer size fields 2 f-13. The LCGi bit indicates whether asecond buffer size field exists for the logical channel group i. Forexample, it indicates whether a second buffer size field exists for LCG1logical channel group 1. If this field is 1, a second buffer size fieldexists for the corresponding LCG. The second buffer size field has an8-bit size and indicates one of the second buffer size indexes between 0and 255. The second buffer size index 0 means that there is no dataavailable for transmission in the logical channels belonging to thecorresponding logical channel group. The second buffer size index 254means that the sum of data available for transmission of the logicalchannels belonging to the corresponding logical channel group is greaterthan the 253rd second buffer size. The second buffer size index 1 meansthat sum of data available for transmission of the logical channelsbelonging to the corresponding logical channel group is greater than 0and less than or equal to the first second buffer size. The secondbuffer size index n (2<=n<=253) indicates that the sum of data availablefor transmission of the logical channels belonging to the correspondinglogical channel group is greater than or equal to the n−1th secondbuffer size and less than or equal to the nth second buffer size. Thesecond buffer size index 255 is not used. The 252 second buffer sizesare defined in the standard.

The logical channel group is configured when the logical channel isconfigured. The logical channel and the logical channel group areconfigured by RRC control messages.

FIG. 2G is a diagram illustrating structures of a third BSR MAC CE and afourth BSR MAC CE, which are priority-based BSRs. The third BSR MAC CEincludes one priority identifier field 2 g-01 and one third buffer sizefield 2 g-03. The priority identifier field has a size of 4 bits. Thepriority identifier field indicates one value between 0 and 15, whichcorresponds one-on-one to the logical channel priority between 1 and 16.That is, adding 1 to the value of the priority identifier field is equalto the actual priority. For example, the priority identifier field 0000means priority 1, 0001 means priority 2, and 1111 means priority 16. Thethird buffer size field indicates a third buffer size index between 0and 15 with a 4-bit size. Unlike the first buffer size index 0 or thesecond buffer size index 0, the third buffer size index 0 means that thesum of data available for transmission of the logical channels having acorresponding priority is equal to or greater than 0 and smaller thanthe first third buffer size. The third buffer size index n (2<=n<=14)indicates that the sum of data available for transmission of the logicalchannels having a corresponding priority is greater than or equal to then−1th third buffer size and less than or equal to the nth third buffersize. The third buffer size index 15 means that the sum of dataavailable for transmission of the logical channels having acorresponding priority is greater than the 15th third buffer size. Thefirst buffer sizes, the second buffer sizes, and the third buffer sizesare predefined in the specification. The 15 third buffer sizes aredefined in the standard.

The fourth BSR MAC CE includes PGi bits and a plurality of second buffersize fields.

PGi indicates whether a second buffer size field of the priority groupidentifier i exists. The priority group consists of at least onepriority, and eight groups could be configured from priority group 0 topriority group 7 in one cell. The priority for each logical channel isconfigured by a predetermined RRC control message received from thefirst NR cell, and the mapping relationship between the priority and thepriority group is configured by a predetermined system informationreceived from the second NR cell. The system information may be SIBX.For example, a list of priorities mapped per priority group may bebroadcast through the SIBX.

FIG. 3 is a flow diagram illustrating an operation of a terminal.

In step 3 a-01, the UE in the RRC_INACTIVE state initiates the secondresumption procedure. The UE may initiate the second resume procedurewhen all of the second resume condition sets are satisfied.

In step 3 a-03, the UE restores the radio bearer configuration and RLCbearer configuration of a specific data radio bearer belonging to thefirst bearer group stored in the UE Inactive AS Context and resumes thebearer.

In step 3 a-05, the UE initiates the second resumption procedure andthen receives the first uplink grant. The uplink grant may be receivedas part of a random access response message during the random accessprocedure or in downlink control information during the second process.Alternatively, it may be a configured grant given in advance inSuspendConfig. The uplink grant includes the size of an uplink MAC PDUto be transmitted by the UE, transmission resources to be used whentransmitting the MAC PDU, and coding information.

In step 3 a-07, the UE generates a MAC PDU. The MAC PDU includes a firstMAC subheader, a first MAC SDU including a first uplink control message,a second MAC subheader, and a second MAC SDU including data of the dataradio bearer. The first MAC subheader is located immediately before thefirst MAC SDU, the first MAC SDU is located immediately before thesecond MAC subheader, and the second MAC subheader is locatedimmediately before the second MAC SDU. The first uplink control messageincludes the UE identifier and resume reason information.

A common control logical channel configuration predetermined in thestandard is applied to the first MAC SDU. Common logical channelconfiguration includes PDCP configuration, RLC configuration and logicalchannel configuration and is as follows.

TABLE 8 Name Value PDCP configuration Not used RLC configuration TMLogical channel configuration >priority 1 >prioritisedBitRateinfinity >bucketSizeDuration ms1000 >logicalChannelGroup 0

In the first MAC SDU, PDCP SDUs to which neither the PDCP header nor theRLC header are added are contained according to the configuration of thecommon control logical channel. The first MAC SDU is given the highestpriority according to the configuration of the common control logicalchannel.

The PDCP configuration and RLC configuration of the data radio bearerstored in the UE Inactive AS Context are applied to the second MAC SDU,and a priority and a logical channel identifier among logical channelconfigurations are applied. Various type of restriction configurationsuch as allowedServingCells in logical channel configuration of the dataradio bearer is not applied to the second MAC SDU.

The common control logical channel configuration predefined in thestandard is applied to the first MAC SDU, and the logical channelidentifier and priority among the logical channel configurations storedin the UE context are applied to the second MAC SDU, and the allowedserving cell list is not applied.

In step 3 a-09, the UE delivers the uplink MAC PDU including the MAC SDUgenerated by applying the predefined configuration and the MAC SDUgenerated by applying the configuration stored in the UE context to thelower layer. The MAC PDU is transmitted by a lower layer.

the MAC SDU generated by applying the predefined configuration islocated before the MAC SDU generated by applying the configurationstored in the UE context.

The MAC SDU generated by applying the predefined configurations isprotected by a security key derived from the security key of the firstbase station, and the MAC SDU generated by applying the configurationsstored in the UE context is protected by the security key derived fromthe security key of the second base station. Protected by keys.

The MAC subheader of the MAC SDU generated by applying the predefinedconfiguration is composed of R bits and an LCID field. The MAC subheaderof the MAC SDU generated by applying the configuration stored in the UEcontext is composed of R bits, F fields, LCID fields, and L fields.

FIG. 4A is a block diagram illustrating the internal structure of a UEto which the disclosure is applied.

Referring to the diagram, the UE includes a controller 4 a-01, a storageunit 4 a-02, a transceiver 4 a-03, a main processor 4 a-04 and I/O unit4 a-05.

The controller 4 a-01 controls the overall operations of the UE in termsof mobile communication. For example, the controller 4 a-01receives/transmits signals through the transceiver 4 a-03. In addition,the controller 4 a-01 records and reads data in the storage unit 4 a-02.To this end, the controller 4 a-01 includes at least one processor. Forexample, the controller 4 a-01 may include a communication processor(CP) that performs control for communication and an applicationprocessor (AP) that controls the upper layer, such as an applicationprogram. The controller controls storage unit and transceiver such thatUE operations illustrated in FIG. 2A and FIG. 2B and FIG. 3 areperformed.

The storage unit 4 a-02 stores data for operation of the UE, such as abasic program, an application program, and configuration information.The storage unit 4 a-02 provides stored data at a request of thecontroller 4 a-01.

The transceiver 4 a-03 consists of a RF processor, a baseband processorand plurality of antennas. The RF processor performs functions fortransmitting/receiving signals through a wireless channel, such assignal band conversion, amplification, and the like. Specifically, theRF processor up-converts a baseband signal provided from the basebandprocessor into an RF band signal, transmits the same through an antenna,and down-converts an RF band signal received through the antenna into abaseband signal. The RF processor may include a transmission filter, areception filter, an amplifier, a mi10r, an oscillator, adigital-to-analog converter (DAC), an analog-to-digital converter (ADC),and the like. The RF processor may perform MIMO and may receive multiplelayers when performing the MIMO operation. The baseband processorperforms a function of conversion between a baseband signal and a bitstring according to the physical layer specification of the system. Forexample, during data transmission, the baseband processor encodes andmodulates a transmission bit string, thereby generating complex symbols.In addition, during data reception, the baseband processor demodulatesand decodes a baseband signal provided from the RF processor, therebyrestoring a reception bit string.

The main processor 4 a-04 controls the overall operations other thanmobile operation. The main processor 4 a-04 process user input receivedfrom I/O unit 4 a-05, stores data in the storage unit 4 a-02, controlsthe controller 4 a-01 for required mobile communication operations andforward user data to I/O unit (905).

I/O unit 4 a-05 consists of equipment for inputting user data and foroutputting user data such as a microphone and a screen. I/O unit 4 a-05performs inputting and outputting user data based on the mainprocessor's instruction.

FIG. 4 b is a block diagram illustrating the configuration of a basestation according to the disclosure.

As illustrated in the diagram, the base station includes a controller 4b-01, a storage unit 4 b-02, a transceiver 4 b-03 and a backhaulinterface unit 4 b-04.

The controller 4 b-01 controls the overall operations of the main basestation. For example, the controller 4 b-01 receives/transmits signalsthrough the transceiver 4 b-03, or through the backhaul interface unit 4b-04. In addition, the controller 4 b-01 records and reads data in thestorage unit 4 b-02. To this end, the controller 4 b-01 may include atleast one processor. The controller controls transceiver, storage unitand backhaul interface such that base station operation illustrated inFIG. 2A and FIG. 2B are performed.

The storage unit 4 b-02 stores data for operation of the main basestation, such as a basic program, an application program, andconfiguration information. Particularly, the storage unit 4 b-02 maystore information regarding a bearer allocated to an accessed UE, ameasurement result reported from the accessed UE, and the like. Inaddition, the storage unit 4 b-02 may store information serving as acriterion to deter mine whether to provide the UE with multi-connectionor to discontinue the same. In addition, the storage unit 4 b-02provides stored data at a request of the controller 4 b-01.

The transceiver 4 b-03 consists of a RF processor, a baseband processorand plurality of antennas. The RF processor performs functions fortransmitting/receiving signals through a wireless channel, such assignal band conversion, amplification, and the like. Specifically, theRF processor up-converts a baseband signal provided from the basebandprocessor into an RF band signal, transmits the same through an antenna,and down-converts an RF band signal received through the antenna into abaseband signal. The RF processor may include a transmission filter, areception filter, an amplifier, a mi10r, an oscillator, a DAC, an ADC,and the like. The RF processor may perform a down link MIMO operation bytransmitting at least one layer. The baseband processor performs afunction of conversion between a baseband signal and a bit stringaccording to the physical layer specification of the first radio accesstechnology. For example, during data transmission, the basebandprocessor encodes and modulates a transmission bit string, therebygenerating complex symbols. In addition, during data reception, thebaseband processor demodulates and decodes a baseband signal providedfrom the RF processor, thereby restoring a reception bit string.

The backhaul interface unit 4 b-04 provides an interface forcommunicating with other nodes inside the network. The backhaulinterface unit 4 b-04 converts a bit string transmitted from the basestation to another node, for example, another base station or a corenetwork, into a physical signal, and converts a physical signal receivedfrom the other node into a bit string.

What is claimed is:
 1. A method by a terminal, the method comprising:receiving by the terminal from a base station a RRCRelease, theRRCRelease includes a first information for second resume procedure, thefirst information for second resume procedure includes a Signaling RadioBearer2 (SRB2) indicator and a Data Radio Bearer (DRB) list; determiningby the terminal a radio bearer configured for second resume procedurebased on the first information for second resume procedure; receiving bythe terminal from the base station a system information, the systeminformation includes a first threshold and a second threshold, the firstthreshold is related to a reference signal received power and the secondthreshold is related to a data volume, initiating by the terminal secondresume procedure; restoring by the terminal configuration of the radiobearer configured for second resume procedure stored in User Equipment(UE) Inactive Access Stratum (AS) context; re-establishing by theterminal Packet Data Convergence Protocol (PDCP) entity of the radiobearer configured for second resume procedure; resuming by the terminalthe radio bearer configured for second resume procedure; andtransmitting by the terminal to the base station a RRCResumeRequest. 2.The method of claim 1, wherein second resume procedure is initiated ifall conditions of a first condition group are fulfilled, the firstcondition group includes the reference signal received power beinggreater than the first threshold and the data volume being smaller thanthe second threshold and a second resume procedure related informationbeing included in the system information, the second resume procedurerelated information includes the first threshold and the secondthreshold.
 3. The method of claim 1, wherein a SRB2 is configured forsecond resume procedure if the SRB2 indicator is included in the firstinformation for second resume procedure, and a DRB in the DRB list isconfigured for second resume procedure.
 4. A terminal in a wirelesscommunication system, the terminal comprising: a transceiver configuredto transmit and receive a signal; and a controller configured to controlthe transceiver to: receive from a base station a RRCRelease, theRRCRelease includes a first information for second resume procedure, thefirst information for second resume procedure includes a Signaling RadioBearer2 (SRB2) indicator and a Data Radio Bearer (DRB) list; determine aradio bearer configured for second resume procedure based on the firstinformation for second resume procedure; receive from the base station asystem information, the system information includes a first thresholdand a second threshold, the first threshold is related to a referencesignal received power and the second threshold is related to a datavolume; initiate the second resume procedure; restore the configurationof the radio bearer configured for second resume procedure stored inUser Equipment (UE) Inactive Access Stratum (AS) context; re-establishPacket Data Convergence Protocol (PDCP) entity of the radio bearerconfigured for second resume procedure; resume the radio bearerconfigured for second resume procedure; and transmit to the base stationa RRCResumeRequest.